Solution:1
In WordPress 3.7, the function wp_debug_mode (defined in wp-includes/load.php, and called from wp-setings.php) sets error_reporting( E_ALL ).
Since wp-settings.php is itself loaded at the end of wp-config.php, you cannot change this setting from wp-config.php (or rather, you can, but it will be overridden).
A solution is to create a “Must Use plugin”, that is to say a .php file located in the /wp-content/mu-plugins/ folder containing :
<?php
if (WP_DEBUG && WP_DEBUG_DISPLAY)
{
ini_set('error_reporting', E_ALL & ~E_STRICT & ~E_DEPRECATED);
}